A majority of the oil wells completed in the Gulf of Mexico are completed in formations which contain carbon dioxide gas. Initial completion of these oil and gas wells requires completion fluids in a weight range from about 8.33 pounds per gallon to about 19.2 pounds per gallon to control the well. These fluids often contain divalent metal compounds such as, but not limited to, calcium chloride, magnesium chloride, barium chloride and zinc chloride which result in the presence of divalent metal cations such as calcium, magnesium, barium or zinc in the fluids to obtain the desired weight per gallon. It is well known that if divalent metal cation containing fluids come into contact with carbon dioxide, there is a very strong potential to form divalent metal carbonate solids or scale. In an oil or gas well, the divalent metal carbonate scale frequently occurs in the perforation tunnels or the tubing to the detriment of the production of oil or gas from the well. A common practice for dealing with such scale in oil and gas wells is to acidize the wells with 5 to 10 percent hydrochloric acid after the initial completion. This technique is successful in removing the scale but involves an additional operation at considerable expense.
U.S. Pat. No. 4,741,400 entitled "Method for Scale Inhibition in a Well Penetrating a Subterranean Formation" issued May 3, 1988 to David R. Underdown; U.S. Pat. No. 4,485,874 entitled "Method for Scale Removal and Scale Inhibition in a Well Penetrating a Subterranean Formation" issued Dec. 4, 1984 to Kevin O. Myers; and U.S. Pat. No. 4,495,996 entitled "Method for Scale Removal and Well Inhibition in a Well Penetrating a Subterranean Formation" issued Jan. 29, 1985 to Kevin O. Myers and Harry L. Skillman, Jr. disclose various processes for removing and controlling scale. An article "Evaluation of Calcium Carbonate Scale Inhibitors for Prudhoe Bay, Alaska" by D. R. Underdown and D. P. Newhouse, SPE 15658 presented at the 61st Annual Technical Conference and Exhibition of the Society of Petroleum Engineers in New Orleans, La. on Oct. 5-8, 1986 also discloses various materials for use as corrosion scale inhibitors.
While many materials have been used to inhibit scale formation previously, none have been fully satisfactory to prevent scale formation in fluids used in well drilling, completion and workovers when the fluids contain calcium, magnesium, barium or zinc cations and when the formation contains carbon dioxide. Since many wells are completed into such formations, a continuing search has been directed to an improved method for preventing the formation of such scale.